Leverage posts-to-posts relationship via frontend posting

Hi All,
Has anyone tackled creating a custom post which leverages posts-to-posts relationship via the front end. Here is what I am trying to do.

I have two custom content type: events and participants
participants can have many events
events can have many participants

From admin, this is working fine via posts-to-posts. However, I need to have users via the front end associate events and participants without having to go through the wp admin site or add events/participants and then associate to participants/events.

http://ww.wp.xz.cn/extend/plugins/posts-to-posts/